A conventional rotation angle detection device, which detects a rotation angle of a rotary member, calculates a rotation angle based on output signals produced by sensor elements. In case that the output signals are a cosine signal and a sine signal, for example, it is required that the cosine signal and the sine signal produced from the sensor elements have a phase difference of 90°. The sensor element for producing the cosine signal and the sensor element for producing the sine signal need be arranged such that the directions of magnetization of the sensor elements are shifted 90°. However, since the direction of magnetization cannot be confirmed visually, it is hard to arrange the sensor elements such that respective directions of magnetization shift 90° exactly. It is therefore proposed in the patent document (JP 4194484, EP 1544579A1) to accurately calculate a rotation angle δ by correcting deviation of arrangement of the sensor elements by subtracting an approximation of trigonometric function from a rotation angle θ detected without phase correction.
According to the patent document, it is required to measure a correct rotation angle δ from an external side in calculating an approximation of a trigonometric function, which is used to correct phase. It is therefore necessary in the patent document to provide an external device for measuring the rotation angle δ. According to the patent document, in case that the number of signals used in calculating the rotation angle increases, it is required to store as many trigonometric functions as the number of combinations of the signals. Thus, storage capacity of a memory will correspondingly increase.